Black Holes in Feeding Frenzy

Top: A gas-rich galaxy collides with a giant galaxy, producing a quasar. Credit: Computer simulation by Joshua Barnes, University of Hawaii.Bottom: Artist’s conception of the heart of a quasar, a massive black hole that sucks in a vortex of gas. Hawaii astronomers found that quasars shine because a giant galaxy with a large black hole collides with a gas-rich galaxy that feeds the black hole. Credit: A. Simonnet, Sonoma State University, NASA Education and Public Outreach.

Two UH astronomers using the Hubble Space Telescope believe they have identified what makes at least some quasars shine: the black hole at the center of a massive galaxy with little gas of its own is gobbling up material from a colliding gas-rich galaxy. The merging of two galaxies has long been thought to be an efficient way of driving gas deeply into a galaxy to feed the central black hole, but there was only indirect evidence for such a mechanism until now.

It was already known that quasars, which are among the most powerful objects in the Universe, lie at the centers of giant galaxies and consist of a massive black hole surrounded by a vortex of gas. Before the gas falls into the black hole, it spins faster and faster, and its temperature rises until it is hot enough to radiate up to a trillion times the power from the Sun.

To answer the question, Fu and Stockton used a telescope-mounted spectroscope to find out what the gas is made of. “We found that the gas that is spiraling into the black hole is almost pure hydrogen and helium, whereas the stars and other material in the surrounding giant galaxy are heavily contaminated by other elements such as carbon and oxygen,” said Fu.

This difference implies that the infalling gas has recently come from outside the galaxy, most likely from another galaxy that is merging with the giant one. Fu and Stockton also see a chaotic distribution of fast-moving patches of relatively pure hydrogen and helium scattered around the quasar, implying that black holes not only swallow things, but can also expel a large portion of their meal out to thousands of light-years away, likely through an energetic blast that happened millions of years ago.

The Institute for Astronomy at the University of Hawaii conducts
research into galaxies, cosmology, stars, planets, and the
sun. Its faculty and staff are also involved in astronomy education,
deep space missions, and in the development and management
of the observatories on Haleakala and Mauna Kea.

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